One type of drill bit used in forming a borehole in the earth is a roller cone rock bit. A typical roller cone rock bit comprises a body with an upper end adapted for connection to a drill string. A plurality of arms, typically three, depend from the lower end portion of the body. Each arm includes a spindle protruding radially inward and downward with respect to a projected rotational axis of the body. A cutter cone may be mounted on each spindle and rotatably supported on bearings acting between the spindle and the inside of an internal cavity defined by the cutter cone. One or more nozzles often are located on the underside of the body and radially inward of the arms. These nozzles are generally positioned to direct drilling fluid passing downwardly from the drill string to the bottom of the borehole being formed. The drilling fluid washes away the material removed from the bottom of the borehole and cleanses the cutter cones carrying the cuttings radially outward and upward within the annulus defined between the bit body and the wall of the borehole.
Each cutter cone generally includes a number of insert bits or tooth bits providing drilling surfaces. It is an advantage for the cutter cone and associated bits to provide high penetration rates, resistance to insert bit or tooth bit wear and breakage, and maximum tolerance to impact and unit loading. An additional feature of some cutter cones are compacts press fitted into the gauge face surface of each cutter cone. These compacts assist with cutting the wall of the borehole as the cutter cone rotates. In conventional roller cone rock bits, compacts generally are oriented such that the axis of each compact is perpendicular to the gauge face surface of the cutter cone.
Examples of a roller cone rock bit having compacts or inserts disposed in the gauge face surface of the cutter cone are described in U.S. Pat. Nos. 4,056,153, 5,145,016 and 5,131,480. U.S. Pat. No. 4,056,153 shows rows of gauge face surface compacts on the cutter cones of a roller cone rock bit. U.S. Pat. Nos. 5,145,016 and 5,131,480 both show bit inserts on the gauge face surface of cutter cones in a roller cone rock bit. Each of these patents disclose compacts or inserts on the gauge face surface of a cutter cone that are oriented perpendicular to the gauge face surface. Each of these patents is incorporated by reference for all purposes within this application.
Conventional compacts typically have a body portion and a cutting portion. The body portion may be the part of the compact press fitted into a hole in the gauge face surface of the cutter cone. The cutting portion of each compact includes the part extending outward from the gauge face surface that engages the wall of the borehole. The cutting portion of conventional compacts is sometimes coated to increase resistance to wearing.
Conventional compacts generally are disposed in the cutter cone such that the axis of each compact is approximately perpendicular to the gauge face surface. With this orientation, the cutting portion of the compacts impinge upon the wall of the borehole such that the side of each compact engages the wall. The force absorbed by the side of each compact causes wear of the compacts and reduces the lifetime of the roller cone rock bit.